Aluminum hydroxide is widely used in the fields such as petroleum refining, chemical engineering, ceramics, building materials, military and defense and the like. Aluminum oxide produced by calcination of aluminum hydroxide is one of the most widely-used catalyst carriers in the field of petroleum refining and chemical engineering, and also a raw material for the production of ceramics, abrasives and the like. There are many processes for manufacturing aluminum hydroxide. For example, bauxite is used as a raw material in traditional processes, undergoing steps such as high temperature calcination, alkali solution leaching, acid neutralization, drying and the like. NaAlO2—CO2 precipitation (which is referred to as CO2 method in short), NaAlO2—Al2(SO4)3 precipitation (which is referred to as Al2(SO4)3 method in short) may also be used. Aluminum hydroxide produced by these methods can also meet use requirements in the fields such as petrochemical industry in terms of the aspects such as specific surface area, pore volume, pore size, adsorption capacity and the like, for example, as hydrogenation catalyst carrier. However, aluminum hydroxides produced by the above methods usually have a low level of purity. Some fields which have high requirements on the purity of aluminum hydroxide, for example, the fields like continuous reforming catalyst carrier, special ceramics, fine chemical engineering, usually require a highly-pure aluminum oxide having a purity of above 99.9%. Aluminum hydroxides produced by the above technical routes cannot meet the above requirement.
A production of aluminum hydroxide by hydrolysis of aluminum alkoxide is an effective route for producing a highly-pure aluminum hydroxide and aluminum oxide. Such a process comprises reacting alcohol with metal aluminum to produce aluminum alkoxide, hydrolyzing the aluminum alkoxide to produce aluminum hydroxide slurry, and drying the slurry to produce a highly-pure aluminum hydroxide powder.
CN85100218A puts forward a process of preparing a highly-pure aluminum hydroxide by hydrolysis of aluminum alkoxide, comprising reacting metal aluminum with isopropanol to produce aluminum isopropoxide in the presence of a catalyst, hydrolyzing to produce aluminum hydroxide, and then calcinating to produce aluminum oxide. The application adopts a hydrous alcohol produced in the hydrolysis of aluminum alkoxide and a low carbon aluminum alkoxide for hydrolysis, dehydrates a hydrous low carbon alcohol to be below 0.2% while hydrolyzing the low carbon aluminum alkoxide, such that it can be recycled for use in the synthesis of the low carbon aluminum alkoxide. However, the process requires a manner of vacuum distillation to separate the low carbon alcohol and the aluminum hydroxide slurry and is highly energy consuming. In the meantime, during the process of vacuum distillation, the unreacted low carbon aluminum alkoxide is allowed for polymerization and decomposition. In addition, the process does not mention a method of recovering the alcohol trapped in the aluminum hydroxide slurry.
U.S. Pat. No. 3,419,352 discloses a process for producing alpha alumina monohydrate. One technical difficulty for the production of aluminum hydroxide by hydrolysis of aluminum alkoxide is that it is difficult to recover alcohols absorbed by aluminum hydroxide. It puts forwards a process of preparing a highly-pure aluminum hydroxide by hydrolysis of aluminum alkoxide. In the process, a small amount of an aqueous solution of ammonia is added during the process of hydrolysis. The content of NH3 in the aqueous solution of ammonia is from 1.8 to 3.4 wt. %. Due to the addition of the aqueous solution of ammonia, the recovery rate of alcohol is increased. Moreover, within a certain range, as the addition amount of the aqueous solution of ammonia increases, the recovery rate of alcohol increases. The recovery rate of alcohol mentioned in the patent may be as high as 99.65%. The biggest disadvantage of this process is that the addition of the aqueous solution of ammonia cannot completely avoid an absorption of alcohols by aluminum hydroxide slurry. A manner of solvent extraction is further required to remove alcohols trapped in the slurry. In the meantime, the addition of the aqueous solution of ammonia often results in that the off-gas emission from industrial devices does not meet the requirement of environment protection.
U.S. Pat. No. 3,773,691 also adopts a hydrolysis of aluminum alkoxide to produce a highly-pure aluminum hydroxide. However, the patent does not use a manner of adding an aqueous solution of ammonia during the process of hydrolysis. It puts forward the following process route: hydrolyzing aluminum alkoxide to produce an aluminum hydroxide slurry phase and an organic phase, separating the slurry phase and the organic phase, then adding an organic solvent to the slurry phase for a further extraction and separation of alcohol in the slurry, wherein the organic solvent is selected from C2-C4 alcohol, then further separating the organic phase for extraction trapped in the aluminum hydroxide slurry through the steam stripping so as to recover alcohol. The process is complicated, involves a long procedure and is highly energy consuming. Meanwhile, the physical property of the aluminum hydroxide is affected to a certain degree due to the steam stripping.
U.S. Pat. No. 3,987,155 discloses a method of producing aluminum alkoxide by reacting metal aluminum with alcohol (C1-C30 alcohol), hydrolyzing aluminum alkoxide to produce an aluminum hydroxide slurry and alcohol, separating the alcohol, filtering the aluminum hydroxide slurry to produce a filter cake, mixing an organic solvent with the filter cake, wherein the organic solvent is selected from the group consisting of ethanol, propanol, butanol, and the organic solvent is added in an amount which can at least azeotropically remove all the water present in the slurry, preferably the organic solvent is added in an amount equal to from 100 to 150 percent of the alcohol amount required to azeotropically remove all the water present. The resulting product has the features of high pore volume and low bulk density. However, the consumption amount of organic solvents while carrying out the process is even larger.